If the ratio is 9:2 that means that 45 would by ñ times 9. At the same time, ñ must also fit the ratio. Using this knowledge, you can divide 45 by 9, giving you 5, then multiply it by 2. This means that the child is 10 years old.
A is the correct answer!
- water can moderate temperature v. well that's why it's used as a cooling agent
- water expands upon freezing (that's why ice floats on water!)
The number of protons and elctrons adds up to the mass number
